Understanding the application

The factors influencing design and choice of a gearbox are numerous, including duty cycle, location, environment as well as space constrictions. The importance of understanding an application to define the optimum drive solution cannot be overstated - as illustrated by just a few projects undertaken by Dana’s engineers.

Efficiency

Dana was commissioned for the Saltend Waste Water Treatment Works (specifically, the replacement of the original EIMCO rake drive system in the lamella tanks), where longstanding odour issues created significant environmental issues. The most obvious choice wasn’t the best solution, as Terjesen explains: “As a general rule, applications in the water industry tend towards high output torque and low (or very low) output speed requirements, which make planetary drives the optimal solution. Most suppliers would consider providing a simple gear unit as a replacement to minimise the risk of problems with specification, design and manufacture, and an in-line planetary unit seems the most obvious selection.

"However, the gear unit is only a small part of the system. There would have to be an output coupling of some form, selected to transmit the output torque required, plus supporting steelwork (which would need access ports to allow bolting the coupling). We wanted to maintain the ‘dry well’ system found in the original installation. With a planetary gearbox mounted directly above the application there is always the risk a standard oilseal could leak lubricant into the process liquid below.” 

Dana’s drive arrangement was far more efficient than the original EIMCO unit, generating the required output from a much smaller prime mover. The drive has an electric motor, a planetary gear unit, a final-stage slew-pinion and bearing, plus supportive steelwork. With no separate method of torque limitation or monitoring specified, Dana proposed to utilise the motor supply current as the generator of the torque level. Terjesen: “While this is, technically, the least accurate position, the total combined drive efficiency of 86% was an improvement over the original drive, thus providing the high efficiency that planetary systems are known for while maintaining the ‘dry well’ system of the original installation.”

Space and safety

For the Hull Tidal Surge Barrier, Dana was commissioned as part of the refurbishment to the 212t gate that protects Hull and the surrounding areas from flood damage. The drive system operating the tidal barrier, spanning 30m, closes approximately 12 times a year against tides reaching up to six metres, and Dana’s solution involved an innovative combination of triple input gearboxes, as Terjesen explains: “The drive system needed to physically fit in a pre-defined and very tight space envelope while accommodating very specific operational needs, and a standard proprietary gearbox wasn’t an option. We specificed a combination of planetary and bevel gearboxes for each tower, a hybrid solution we were able to supply based on our extensive product portfolio, and one which gives a reduction ratio of over 1550:1. This innovative arrangement allows for mechanically linking both drives with the option to hydraulically or hand drive the gate from either tower, while keeping dimensions to a minimum. Looking at different scenarios, for example lifting the gate when it is subjected to mud suction, we designed a solution to fit within the confines of the tower and to operate safely even in the event of a complete power failure.”

Reducing complexity

The refurbishment of the Woolwich Ferry linkspans, the loading bridges that allow for access across the River Thames, demonstrates the benefits that expertise can bring when considering drive and gear options.  With 160 tonnes of operating equipment, including obsolete and unreliable lifting systems, Dana’s solution involved an innovative application of planetary gearboxes. TfL wanted increased reliability, while reducing long term cost, and Dana’s solution dramatically reduced the complexity of the system. The counterbalance system was re-engineered and now functions as the lifting system and the linkspans are now raised and lowered by rotating new, stronger, counterbalance shafts. This was made possible by replacing the old counterbalance shafts with new assemblies directly coupled to new drive system gearboxes. The new electric drive motor units are fitted to bespoke carrier assemblies which link the motors, via four stage planetary gearboxes and couplings to the counterbalance shafts.

“The innovative use of Dana’s S Series planetary gearboxes incorporated technology commonly used in the wind power sector, with high torque density which reduces the overall space requirement and provides good value performance.  Not normally considered for projects such as the Woolwich Ferry refurbishment, these planetary gearboxes brought major space- and cost-savings to the new lifting system.  At approximately 1/5th of the size of the previous system, the S Series gearboxes introduced a degree of flexibility to the project – far less complicated than the original lifting system," says Terjesen.

Martin Terjesen is Dana SAC UK’s technical manager

www.DanaSAC.co.uk